Phylogenomic identification and overexpression of plant size–related genes in Setaria viridis and rice

Plant size is a critical component of agricultural productivity as larger plants produce more biomass. To identify genes related to plant size, we grouped C₄ grasses into small and large and used OrthoFinder to find orthologous genes present in large but absent in small grasses. Three such genes were identified from sorghum (Sorghum bicolor [L.] Moench) by phylogenomic approach, and they encode nitrate transporter (Sobic.007G213200), oxysterol binding protein (SbRio.01G578800) and thioredoxin reductase (SbRio.05G168300), respectively. Overexpression of all three genes driven by the maize ubiquitin promoter in Setaria viridis (L.) Beauv. indicates that they all affected plant size as measured by plant height and tiller number. Both nitrate transporter and oxysterol binding protein increased plant height and tiller number, and thioredoxin reductase significantly decreased tiller number but had minimal effect on plant height. In rice (Oryza sativa L.), all three constructs reduced plant height significantly. The only commonality between the transgenic species was that nitrate transporter and oxysterol binding protein increased tiller number in both S. viridis and rice. Overall, we have demonstrated that phytogenomic approach can be used to identify genes responsible for large plant size in the grasses.